internal/cpu: make all constants for s390x feature detection typed

Only the first constant in the function and facility
constant declaration blocks were typed constants.
Make all other constants used for function codes and
named facilities also typed.

Change-Id: I1814121de3733094da699c78b7311f99ba4772e1
Reviewed-on: https://go-review.googlesource.com/126776


Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>